1. Field of the Invention
This invention relates, generally, to punches which are used to perforate sheet goods and, in particular, to hand held punch and die tools that are used to perforate the margins of sheet metal, fiber glass, plastic strips and heavy fabric or cardboard.
2. Discussion of the Relevant Art
In the industry with which I am involved, sheet metal repair and fabrication, a need has developed for a hand held tool that can be used to easily perforate the margins of sheet metal, disposing therein a series of holes having differing sizes. The particular need which I have sought to satisfy (in use of the instant invention) is to place, in the margin of sheet metal or similar goods, a set of three holes in central alignment. The purpose of these holes is to provide a receiving port at the center of the set for a DZUS (TM) type sheet metal fastener stud (on fitting), while the adjacent two holes are used to receive pop rivets, or similar apparatus, for the purposes of placing over and behind the central hole a sheet metal fastener wire bracket which serves to receive and capture a portion of the sheet metal fastener bolt.
In the course of business, it is necessary to replace portions of an automobile body with panels, aluminum sheets, that are cut from 4 ft..times.8 ft. sheet metal stock. The panels are replacements and access panels for race cars, stock cars, go carts and the like. Sheet metal already on the car is referred to hereinafter as base or foundation (metal). During replacement of a panel on one of the subject vehicles, it is the custom to place the (replacement) sheet over a port in, or damaged area, of base metal so that substantial portions of base sheet and replacement marginally overlap. The replacement sheet has been prepared with holes through which the DZUS shank can pass, but the head cannot. The foraminous replacement sheet margin is placed over the base sheet margin and scribe or bench marks are placed at the center of the holes onto the base margin. Then, a template is used to drill holes for the DZUS shank and two straddling holes for the pop rivets, by which a DZUS retaining spring is attached. The drilling is tedious and can be readily avoided by use of a punching tool.
In U.S. Pat. No. 4,033,037, a method and a means for punching sheet goods are disclosed. A device for punching a plurality of holes adjacent the edge of one or more sheet members is shown that comprises a pair of elongate jaw members pivotally joined intermediate their length in "scissors-like" fashion. Here, two first class levers are disclosed sharing a common pivot-fulcrum so that, upon squeezing the handles thereof together, the jaws are caused to close, resulting in a typical punch-die machination. A punch is carried on one end of one jaw member and an aligner is positioned in side by side relationship to the punch, in a fixed, spaced relationship therefrom. The die matrix is carried by the other jaw member to receive the punch tool. Thus, only two tools are apparent in the '030 punching device, and one is used solely for the purposes of aligning the other. Intermediate the punch and the die matrix, is a stripper device consisting mainly of a thin, perforated tab that is used to restrain the sheet material as the jaws are opened and the alignment and punch tool are withdrawn from the die matrix. The '037 device fails to meet my immediate needs in that the alignment tool is superfluous and the opposed first class lever of the tool is insufficient for applying the kind of punching force that I require in my trade. A locking hole punch is disclosed in U.S. Pat. No. 4,707,924, that comprises an arm member having a head at the end of an outwardly curved portion and a first handle extending from that curved portion. A first lever member formed in a generally mating, outwardly curved configuration is pivotally connected to the arm at the top of the arm handle at a first pivot. A generally straight second lever, which acts as a second handle spaced from the arm handle, is pivotally connected to the first lever member at a second pivot with the first pivot. A toggle member is connected to the second lever at a third pivot and to the arm handle at a fourth pivot. When the arm and second handles are pressed together, the toggle member is driven so that the second, third and fourth pivots are moved into a straightline alignment and the punch, which includes a punching pin, is driven into a working position with a head. The toggle member can be further driven into a locked mode, which is releasable by operation of a toggle release device. The force application system of the '924 device is essentially a first class lever system. When this lever system is operated, the toggle member moves forward and toward the stationary arm of the tool allowing the first class lever system to close the pin-carrying jaw and, by an over-center motion lock or clamp to the arm member. The disadvantage of this form of mechanism, for my purposes, is that the patentee was more concerned with locking the punch member after the driving action, thus, there was no immediate requirement for a forceful punching action. The use of the first class lever system would be ideal in force transmission but for the fact that its application point (of rotation of the punching jaw) is too close to the common fulcrum that is used for pivotation of the jaws. Such a location negates the value gained in force multiplication through use of the first class lever system by compounding it with the third class lever system of the jaws. In most applications where one seeks mechanical advantage, the third class lever system simply does not have the effect of the first or second class lever systems. Further, once over center, the locking mechanism of the '924 tool would be highly disadvantageous since it is the premise in my form of work that the faster the holes may be punched, with the least amount of action, the better for the fabricator and the customer. A metal clipping tool disclosed in U.S. Pat. No. 3,505,714, is composed of a pair of lever arms, a fulcrum pin connecting the pair of lever arms together near one end, each of the pair of arms having an outwardly diverging crank at its connected end, a pair of jaws hingedly connected together, a pivot pin connecting each of the pair of jaws to a crank, the pair of jaws having free ends and opposing inner edges, a material clipping number carried by the free end of each of the pair of jaws to project inwardly of the opposing inner edge of the jaw, one of the material clipping members being a punch and the other of the members being an anvil, having a recess to receive the punch, and the punch and anvil being shaped to provide cooperating means that are adapted to form a substantially rectangular puncture in contacting structural members. In this tool, the lever arms are fulcrumed for first class leverage. The '714 tool has a distinct mechanical advantage over the tools of '037 and '924; but, the advantage of compounding first class levers is offset by the fact that the jaws used to carry the punch and die matrix of this tool are placed on very short levers and, therefore, no great mechanical advantage is gained. Further, when the tool handles are spread apart, the jaws actually extend forward of the common fulcrum and present a problem when one attempts to manipulate them into an alignment for rapid punching. Another disadvantage of the '714 tool is that no means are provided to restrain the punched metal as the punch is withdrawn; that is, there are no stripper means provided with the device.
Finally, U.S. Pat. No. 4,753,010 discloses, as an alternate embodiment, a tool consisting, essentially, of a bifurcated lower lever arm holding a guide and retainer means in the upper branch thereof for a sliding, vertical tool, which is brought into contact with an anvil on the lower branch of the bifurcated arm. The driving force for the sliding tool is a lever, working on the second class lever principle, that is fulcrumed or pivotally hinged to the extended upper branch of the bifurcated arm. As in the previously discussed art, the '010 tool remains deficient for my purposes. The patentee does not teach how the apparent arcuate motion of the upper arm would be translated to a purely linear motion in order to allow the cutting tool to remain in proper punching alignment. Another deficiency is the fact that the pivotal connection of the sliding tool with the upper arm lever is displaced too far rearward of the fulcrum to gain any significant mechanical advantage, being that this is a second class lever system. Finally, no stripper means are provided in order to withdraw the tool cleanly from a workpiece.
The deficiencies of all available cutting tools has caused me to develop my own special apparatus for perforating sheet metal with the particular three in-line holes that I require in my work. Up until now, the requisite perforations have been made in the receiving sheet metal foundation by use of scribing and physically drilling (generally by hand) the necessary holes.